Transparent electronics is an emerging and promising technology for the next generation of electronic and optoelectronic devices. Transparent devices have been fabricated for various applications, including transistors, optical circuits, displays, touch screens, and solar cells. However, the battery, a key component in portable electronic devices, has not been adequately demonstrated as a transparent device. Consequently, fully integrated and transparent devices cannot be adequately realized because the battery occupies a considerable footprint area and volume in these devices. Typically, a battery includes electrode materials, current collectors, electrolyte, separators, and packaging. None of these components are typically transparent except for the electrolyte. Furthermore, as these components are typically in series, all of these components should be clear to make the whole device transparent. A conventional approach for making transparent devices is to reduce the thickness of active materials to much less than their optical absorption length, as demonstrated in carbon nanotubes, graphene, and organic semiconductors. However, this approach is not suitable for batteries, because active battery materials typically do not have an absorption length long enough in the full voltage window. For example, LiCoO2 and graphite, the most common cathode and anode in Li-ion batteries, are good absorbers even with a thickness less than 1 μm. Moreover, conductive carbon black additive is generally included in electrodes, which occupies at least 10% of the total volume. To power common portable electronic devices, the total thickness of electrode materials should be on the order of 100 μm-1 mm, much thicker than the absorption length of the electrode materials. This dilemma comes from the relationship that the transparency of materials typically decays exponentially with the thickness, whereas the amount of energy stored typically increases linearly with the thickness.
It is against this background that a need arose to develop the transparent electrochemical energy storage devices and related methods and systems described herein.